The correct answer is B) They are gravity-fed. Centrifugal pumps aboard tankers are not gravity-fed. Instead, they rely on the impeller design to create suction and push the fluid through the system. Centrifugal pumps are commonly used for cargo handling, ballast, and stripping operations on tankers, as they are well-suited for these high-volume, low-pressure applications. The other options are incorrect. A) Centrifugal pumps are generally less expensive than reciprocating pumps. C) and D) Centrifugal pumps are indeed used for stripping pumps on tankers, but this is not the key distinguishing feature.